Below are the status readings of the amp while the voltage map of the JCM25 main board is being measured. Please adjust your amp according to these values. Due to slight variations in electronic components, a 10% fluctuation between the voltage values measured from your amp and the data in this voltage map is normal..
Voltage: DC
Standby ON
Contol: Gain and Master minimum
Biase voltage: -30V
Power tube: Pentode
DC voltage map of main board
Filter circuit of power
Let us see the circuit board from the side which installed components. Down to up ,the power supply filter circuit is on the bottom of the board. The rightest is the rectifier bridge consisted by four diodes D1-D4, which provides full-wave rectify for 260 VAC from power transformer. From right to left, through different capacitors filting , the different plate voltages of the tube in amp stages are : B+A: 390VDC, B+B: 360VDC, B+C: 308VDC, B+D:270VDC (V2). B+E:255VDC (V2).
If you could not hear any sound after turning on amp, please make sure these voltage normal first, then check the pins connected with them in tube sockets.The plates of 12ax7 are Pin 1, 6.The plate of 6L6 is Pin 3.
Position code
The topmost row of the main board contains holes, each labeled with a position code consisting of one letter and two digits. The first letter, 'V,' represents 'Valve (Tube).' The first digit indicates the tube number, and the second digit represents the tube pin number. For example, 'V2-3' means this hole should be connected to Pin 3 of the second tube.
Since this main board is a universal board for our amps, the position codes printed on the board may not fully match the actual layout drawing of each amp. Please connect the wires according to the layout drawing specific to each amp kit.
First preamp
BFLEX25 has only two amplification stages: V1B and V1A. The voltages of V1 are as follows: The plate voltage of V1B is 149V DC (V1-6 on the board). The plate voltage of V1A is 144V DC (V1-1 on the board). The cathode voltage of V1B is 1.6V DC (V1-8), and the cathode voltage of V1A is 1.3V DC (V1-3).
Long Tail Pair phase inverter
The second 12ax7 is Long Tail Pair(LTP) phase inverter of BFLEX25 amp.The grids (Pin2,7) of V2 connected with SKY and V2-8 of the board, the voltages of these two holes are 0VDC. The plates( Pin1,6) of V2 connected with V3-1 and V3-6 of the board.The voltage of V3-1 is 211VDC and V3-6 is 190VDC. The cathodes of V2 are Pin 3 and 8 of tube, they connected with one hole of the board V3-3/8, the voltage is 1.6VDC.
The power tube of BFLEX25 can use 6L6 or EL34 etc. The datas in the voltage map were measured by 6L6. Pin2 and 7 are pins of filament. Pin3 is Anode(Plate). The Pin 4 is grid2(Screen). Pin5 is grid1.Pin8 is cathode and beam plate. The type of power amp stage of BFLEX25 is Class AB : V3 and V4. The pins of these two 6L6 connect with the main board include: Pin2s(Filament)of V3 and V4 connect with board 6.3VAC; Pin4s(grid 2) of V3 and V4 connect with V4-9,V5-9 of the board, the voltages are 330VDC all; Pin5s(grid 1) connect with V5-2 and V4-2 of the board, one is -43VDC, one is -40VDC; Pin8s (Cathode) connected with V4/5-3 and R24C of the board, all are 80 mVDC.
The static operating points is important parameters describing status of amp, it is useful tool to troubleshoot. Abnormal operating points always means not only connection in mistake, but also possibility of resonance in the circuit.